A plate-type heat exchanger for heat exchange between two fluids is formed of a stack of plates shaped to form two independent sets of normally transverse passages through which respective fluids can be passed. The plates are thermally conductive so the warmer fluid can heat the cooler one.
The basic type of such a heat exchanger is described in German patent publication No. 2,226,056, where the exchanger is intended for use principally as a condenser in a household clothes dryer. It has a stack of thin metal plates separated by rigid rails to which these plates are bonded to form a set of coolant passages and an independent set of moist-air passages. The entire assembly is held in a frame that may form the separating rails, or each plate may be held in its own frame.
Another standard heat exchanger of the plate type is seen in U.S. Pat No. 3,454,082. Here two passages are formed between a plurality of identical plates, with every other plate extending at a right angle to the two plates sandwiching it. These plates are metallic and the exchanger is intended for use with liquids.
Variations on these styles abound. German patent document No. 2,706,003 has three-part plates with throughgoing holes. British patent No. 2,028,996 describes a system provided with special seals between the plates. In German patent publication No. 2,634,476 a stack of adjacent profiles is used. German patent publication No. 2,332,047 has hollow plates formed with ribs for use in a boiler. In French patent No. 998,449 the plates form inclined flow passages, while German patent No. 434,787 has so-called zigzag passages.
The problems of these known systems have three principal sources: the material of the plates, the rigidity of the entire assembly, and the connection and sealing between the plates and the surrounding frame.
The material of the plates is usually metal. As such the plates are usually strong and highly thermally conductive. Nonetheless unless expensive alloys are used, the plates are subject to corrosion and therefore have a short service life. Furthermore appropriately shaping the metal plates can be quite difficult, especially when an extremely tough alloy is employed.
A corrosion-resistant synthetic resin can easily be given any desired shape. Nonetheless it is necessary to make the plates relatively thick to obtain the necessary rigidity, and since most resins are poor conductors of heat, such thick plates greatly reduce exchanger efficiency. In addition the sealing and mounting problems of the metal plates are not overcome in the synthetic-resin plates.